The purpose of stabilizers for polymers is to prevent deterioration of the polymers during processing at high temperatures, and also to permit manufacture of products with increased intrinsic quality because of the enhancement of their resistance to thermal and light degradation during use. In addition, because of the ability of these products to withstand more rigorous conditions, their versatility is increased and new areas of application are thereby opened.
An important class of polymer stabilizers are the organic phosphites. They include, as two especially useful groups, the dialkylpentaerythritol diphosphites and the polyalkyl bisphenol-A-polyphosphites. They are used widely in the stabilization of vinyl chloride polymers, polyolefins and styrene polymers such as ABS. The dialkylpentaerythritol diphosphites have the structural formula: ##STR1## where R and R' are alkyl groups. The polyalkyl bisphenol-A polyphosphites have the structural formula: ##STR2## where A and B are each HOC.sub.6 H.sub.4 C(CH.sub.3).sub.2 C.sub.6 H.sub.4 O or RO. R is alkyl and n is 1-5.
Despite such wide usage, however, these types of stabilizers have not been entirely satisfactory, because of their own slight instability on storage. They tend to absorb moisture from a moist environment and their effectiveness as stabilizers for polymers seems to decline in direct proportion to the amount of water absorbed.
This disadvantage can be avoided by taking care to store and transport the stabilizer only in a dry atmosphere. Once incorporated in a vinyl polymer composition, no problem is presented apparently because of the essentially anhydrous condition of such polymer compositions.
Obviously, though, elimination or at least amelioration of the problem is desirable. A moisture-insensitive phosphite stabilizer will preclude the many inconveniences and expense associated with having to maintain an anhydrous environment.
U.S. Pat. No. 3,553,298 (Hodan) shows the stabilization of phosphite esters broadly by using any of several classes of amines including triisopropanol amine. See column 2, line 24 and Examples I-VI.
M. C. Imaev, Zhurnal Obshchei Khim. 31, 1767-70 (1961) shows the stabilization of lower trialkyl phosphites with organic and inorganic bases. The organic bases shown include pyridine, triethyl amine and dimethyl aniline.
U.S. Pat. No. 2,114,866 (Vaughn) shows the stabilization of esters of inorganic esters with an amine. While Vaughn is interested primarily in organic silicates he does mention also (see page 2, column 2, lines 17-22) borates, phosphates, "symmetrical" phosphites, arsenates and symmetrical arsenites.
U.S. Pat. No. 3,787,537 (Marcq) discloses a class of phosphite esters which are said to be stable to hydrolysis. Marcq refers also (see column 2, lines 9-10) to the stabilization of previously known phosphites by "a small quantity of a heavy amine, usually triisopropanolamine (French Pat. No. 1,582,387)". The cited French patent is a counterpart of the above Hodan et al U.S. patent.
None of the above disclosures, however, deal with the type of specific phosphites which are rendered resistant to hydrolysis by the invention.